1. Field of the Invention
The present invention relates to a security alarm system by which emergencies, such as unauthorized intrusions, destruction or removal of property by intruders, fire, and failure of equipment, are detected in a predetermined guard area and a detected signals are transmitted from said predetermined guard area to a central station.
2. Description of the Prior Art
Conventional security alarm systems such as disclosed in Japanese Unexamined Utility Model Publication No. 57-123594, comprise a plurality of sensors for detecting emergencies in a predetermined guard area, a means for converting the emergency data of the sensors into electric signals, and a security controller for transimitting the electric signals to a central station through cable or by radio.
The use of wire necessitates complex wiring work between the sensors and security controller and is problematical in that the resultant system is more expensive and takes longer to install than with radio transmission. Also, wiring works tends to detract from the aesthetic sense of the installation area.
On the other hand, the use of radio transmission, while better than wire in these regards, is problematical in that the system is then designed based on one-way transmission of signals from the sensors. Should the sensors or other transmitters which are connected to the sensors by wire and transmits signal from the sensors be destroyed or removed by intruders or break down, the security controller would assume a normal situation exists even in the event of emergencies.
Some sort of continuous transmission of signals from the sensors to the security controller may be considered, but this would entail greatly increased power consumption.